Verse 5 quotes, with slight modifications, Isaiah 29:10. The use of this verse is important for two reasons. The first is that it applies to the last days when humankind is spiritually asleep. In Isaiah, the sleep follows up on the image of the hungry man who only eats in a dream. Iniquity has closed their eyes so that they do not see.
What is important in Nephi’s context is that this has led to the rejection of the prophets and the unbelief in the seers. In particular, the mention of the seers should resonate with the coming forth of the Book of Mormon. It is therefore not surprising that right after noting the rejection of prophets and seers, Nephi no longer quotes Isaiah, but expands Isaiah into the context of Nephi’s vision of the last days in which the words of his people would come to the gentiles.
Isaiah, verse 11, mentions that a book will be brought, but the rest of Nephi’s sentence is his own contextualizing.